Reducing the use of critically important antimicrobials in veterinary medicine is increasingly important to avoid the development and spread of antimicrobial resistance. The aim of this study was to analyse ten-year trends of colistin consumption in Estonia and to ascertain the possible association between Escherichia (E.) coli vaccination and colistin consumption in pig production. Colistin sales data (2010–2019) were collected from the wholesalers, allowing differentiation of target species. In Estonia, the amount of sold colistin increased constantly and almost doubled from 2010 to 2013, and decreased from 2013 to 2019 by 92.5% in total. On average across a ten-year study period, 89.7% of colistin was used in pig production. The number of sold doses of E. coli vaccines for pigs was very low before 2014 (<2000) and increased drastically to 2019 (362,000). According to linear time-series model with autoregressive integrated moving average (ARIMA) the consumption of colistin in pigs decreased on average by 0.23 mg/PCU for every 10,000 E. coli vaccine doses (95% CI −0.39, −0.06; p = 0.006) over ten years. This study revealed that in pig production, vaccination against E. coli strains contributes to the expected downward trend in colistin consumption.

Clinical mastitis (CM) is the most common microbial disease treated in dairy cows. We analyzed the antimicrobial usage in cows with CM (n = 11,420) in large dairy herds (n = 43) in Estonia. CM treatment data were collected during a 12-month study period. The antimicrobial usage was observed during the 21 days from the initiation of treatment, and the incidence of antimicrobial-treated CM was calculated for each study herd. The effect of intramammary (IMM), systemic, and combined (systemic and IMM) penicillin treatment of CM on the post-treatment somatic cell count (SCC) was analyzed using the treatment records of 2222 cows from 24 herds with a mixed multivariable linear regression model. The median incidence of antimicrobial-treated CM was 35.8 per 100 cow-years. Procaine benzylpenicillin and marbofloxacin were used in 6103 (35.5%, 95% CI 34.8–36.2) and 2839 (16.5%, 95% CI 16.0–17.1) CM treatments, respectively. Post-treatment SCC was higher after IMM penicillin therapy compared to systemic or combination therapy. Treatment of CM usually included first-choice antimicrobials, but different antimicrobial combinations were also widely used. The effect of procaine benzylpenicillin to post-treatment SCC was dependent on the administration route, cow parity, and days in milk. Further studies should evaluate the factors affecting veterinarians’ choice of antimicrobial used in the treatment of CM.

Objectives In the absence of authorized veterinary medicinal products, veterinarians can use authorized human medicines, if necessary. The number of registered veterinary medicinal products, including veterinary antibiotics, has increased, over the years. Reducing the use of medically important antimicrobials in veterinary medicine is increasingly important to avoid the development and spread of antimicrobial resistance. The aim of this study was to analyse 17 year trends in the use of human antibiotics in veterinary medicine, in Estonia. Methods The data of human antibiotics used in veterinary medicine are based on wholesaler’s reports collected by the Estonian State Agency of Medicines, in 2006–2022. The sales data include total sales of human antimicrobial medicinal products to veterinarians and are collected at package level per year, including the name of the medicinal product, identification number of the product, active substance, pharmaceutical form, strength, package size and number of sold packages. Results Between 2006 and 2022, the overall sales of human antibiotics to veterinarians increased from 40.6 kg in 2006 to 54.4 kg in 2022 (peak 71.6 kg in 2019). In Estonia, based on 17 years of data, 220 different human antimicrobial medicinal products were sold to veterinarians, an average 91 different products per year (range 79–101). The number of different human antibiotic substances used in veterinary medicine was 45 ± 2 per year, 60 in total. The most used antibiotics over the 17 years were orally administered amoxicillin, clindamycin, ciprofloxacin, sulfamethoxazole and doxycycline and injectable amoxicillin and cefazolin. The turnover of human antibiotics sold to veterinarians increased from 34 000 EUR in 2006 to 99 000 EUR in 2022. Over the years, analysed by the product form, the most sold human antibiotics for veterinary use were products for oral administration, accounted for 90% of total quantity of antibiotics (24 different substances), followed by injections (9%, 19 different substances) and dermatological and sensory preparations (0.6%, 7 and 9 different substances, respectively). From medically important antibiotics, meropenem, imipenem, piperacillin, ceftriaxone, vancomycin and mupirocin were used in small quantities throughout the years. Conclusions Despite the number of registered veterinary antibiotics having increased over the years, the consumption of human antibiotics used in veterinary medicine has increased by the total quantity and by the turnover. The number of human antibiotic substances and sold packages has no significant changes.